When aircraft are used for covert purposes, such as for reconnaisance, weapons delivery and the like, some form of camouflage is desirable to avoid detection. Defense systems involving radar, thermal and acoustic detection means in various combinations have made it difficult to make aircraft undetectable. Radar has the longest range and most versatility of the detection devices and is therefore of prime consideration. Decoys can be used, but must be carried by the aircraft and are only temporary.
Various techniques have been developed to minimize detection of aircraft, such as by using non-metallic materials for large portions of the structure. However, this structure is transparent to radar and all internal metal structure, such as the propulsion means, electrical components and the like, provide readily recognizable return signals to radar. Certain materials have been developed which effectively absorb radar energy, but are limited in structural use. In conventional air craft design there are many different surfaces and edges which produce radar signatures that are recognizable as being from an aircraft. In addition, other devices are capable of detecting thermal and acoustic energy from the aircraft's propulsion system. To avoid detection, all such sources of energy emission must be shielded and the airframe must be adapted to minimize the radar cross section.